The most obvious conflict in the plot of "All Summer in a Day" is the external conflict between Margot, a relative newcomer to life on Venus, and the other children, who were born on Venus and live in its constant rain and gloom. The children, born to "rocket men and women" whose job it is to create a place for people from Earth to live on Venus, have only ever experienced the sun for two hours of their entire lives. Further, they do not remember it because they were only two years old at the time. Margot came to Venus after living her early childhood years on Earth. After four years on Venus, she still remembers the experience of sunlight. The conflict between them exists due to this difference in their experiences and the apparent jealousy they have toward Margot.

The resolution of this conflict arrives on the one day in seven years that it finally stops raining and the sun starts shining for two hours. The conflict between the children and Margot centers on her knowledge of the sun and clarifying misconceptions for the children. They are angry at her knowledge and end up locking her in a closet just before the rain stops. The children run out into the sun, and only after two joyful hours of experiencing it do they realize that they left Margot locked in the dark closet the entire time the sun shone. Only then do they appear to feel guilty and let Margot out, resolving the conflict of her having been locked in the closet. By their feelings of guilt we see that perhaps the conflict of their anger toward her is also resolved. This passage in the story reads as follows. 

"They walked over to the closet door slowly and stood by it. Behind the closet door was only silence. They unlocked the door, even more
slowly, and let Margot out."

What is the main conflict in Ray Bradbury's "All Summer in a Day"?

The main conflict in the story is between Margot, a child who has relatively recently moved to Venus from Earth, and the other children in her class. The story takes place on Venus, a planet of constant rain, except for a few hours every seven years, when the sun briefly comes out. Margot is withdrawn and poetic, and refuses to play the games the other children enjoy. But her real crime is memory: "that she had come here only five years ago from Earth, and she remembered the sun and the way the sun was and the sky was when she was four in Ohio. And they, they had been on Venus all their lives, and they had been only two years old when last the sun came out and had long since forgotten the color and heat of it and the way it really was." Margot's memory of the sun, in a sense, is her memory of being human. When the children lock her in a closet and forget about her during the time when the sun finally comes out, it is as if they are trying to erase, or deny, her humanity. The story ends, however, without any resolution to this conflict: what Margot does, after they let her out of the closet, is anyone's guess.